TRANSPORT OF FISHES ^J 



is a good stand-by method and for some transport 

 facilities may constitute a desirable supplement to 

 other aerating devices. 



Agitation by baffles dependent upon the movement 

 of the transport unit is obviously of supplementary 

 value. Aeration by circulation, w^hich usually involves 

 withdrawing the water from the bottom of the tank 

 and spraying it back on the surface, also eliminates 

 considerable carbon dioxide and ammonia and makes 

 possible filtration. Mechanical agitators widely used 

 in the transport of bait minnows are available in 

 models that operate on 110- volt domestic current or 

 12-volt automotive current. As a simple, fool-proof 

 piece of equipment that can hardly be improved on, 

 the author considers them the most satisfactory 

 aerating device for aU size tanks. 



Carbon Dioxide 



When fishes are crowded, carbon dioxide can 

 accumulate rather rapidly. Higher concentrations of 

 carbon dioxide interfere with the fishes' utilization of 

 oxygen and cause a decrease in pH. Fish exhibit signs 

 of anesthesia at 40 to 50 p. p.m. carbon dioxide, and 

 McFarland and Norris (1958) demonstrated delayed 

 mortality that appeared to be associated with con- 

 centrations even below 20 p.p.m. McFarland and 

 Norris also investigated the control of decrease in pH 

 during transport by the addition of tris-hydroxy- 

 methyl-aminomethane referred to as "tris-buffer." 

 They considered that the decrease in pH during trans- 

 port is primarily a result of an increase in carbon 

 dioxide. 



Upon addition to water, tris-buffer produces a pH of 



